Klipsch anechoic chamber turns 40 years old

[Arkytype]

About 40 years ago I drove to the Hope plant to see the anechoic chamber I heard was under construction. When I got to the new lab, I was startled to see Paul rotating (OK, he was spinning) the corner turnstile as fast as he could by hand. I remember feeling the rush of air as each quadrant's dividing wall sped past. He probably "aged" the bearings 20 years in 20 minutes! I don't remember who else was there at that moment but Paul was obviously in his element smiling and telling how the "door" was conceived and constructed. I believe he told me the vertical shaft had Ford truck axle bearings at the top and bottom. Maybe Jim Hunter can fill in here.

 

I've attached two relevant documents written about forty years ago; the AES paper,  Anechoic  Chamber with Optional Boundaries co-authored by James R. Hunter and Paul W. Klipsch (Note Paul gave Jim top billing); U.S. Patent 4,387,786 titled Anechoic Chamber Arrangement, also co-authored by Paul & Jim.   

 

Lee 

Chamber patent.pdf AES Paper.pdf

[CECAA850]

I've been in it a few times.  It's pretty cool.  If you fart in there no one can hear it however it can still be detected...............

[babadono]

I think Chief told us a story about helping to change those bearings. Kinda real and kinda fun but not real fun.

[babadono]

"We fully expect that the new chamber will open up a
whole new region of difficulties, but that some of the
 things will be useful."

Quote from the AES paper,  yep that's Paul Wilbur Klipsch.
 

[OO1]

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[Coytee]

Very interesting. I would’ve thought that it was many years older than that. Is that the age of the chamber itself or is that the age of them altering the chamber and adding that rotating door?

[OO1]

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[Ceptorman]

5 hours ago, Randyh said:

how does this chamber compare to others in the industry ,as we speak -- is it the only one of it's kind -

Klipsch has one at the HQ in Indy, I'm sure there are many scattered across the country.

[Coytee]

Do they all have “the door” or is there a more traditional design?

[glens]

I'd guess the rotatable 1/4 pi is novel.

 

What I'd like to know is how often is it dusted?  I'm thinkin' over 40 years, dust accumulation would affect the absorption abilities appreciably...

 

Does Roy, or one of his lackeys, periodically hit the wedges with a shop vac?

 

And do they cover the grating for measurement-taking?  'Cause that will surely affect the echoic behavior in the room.

[babadono]

4 hours ago, glens said:

And do they cover the grating for measurement-taking?  'Cause that will surely affect the echoic behavior in the room.

Not sure about a true and correct answer to this question. But have you ever been in it? It's SPOOKY. They will not even turn out the lights when visitors are there for fear some will loose their balance, get disoriented and fall and injure themelves or others.

[PrestonTom]

Although I am not Roy, I can address some of the points raised above. 

 

No need to worry about the dust. It will have a negligible effect. However there is a concern about whether the wedges have mold or mildew on them. It is infrequent, but can be a real headache. 

 

In many chambers, the aluminum grating only covers a portion of the floor and is frequently removable (2x 4 ft grates resting of pillars anchored to the concert floor that is many feet below). The alternative a suspended steel cable floor (which needs to re-tensioned periodically over the years). Even with the grating in place (not even covered), the impact on the measure may be minimal (depends on location and what portion of the spectrum you are interested in). 

 

Many chambers are only semi-anechoic and have a concert floor so you can drive heavy equipment or vehicles inside. 

 

There are different designs on doors. Some are actually filled with sand and have very exotic rubber seals/gaskets. Remember that anechoic chambers need to be relatively "sound proofed" also. This is always a problem area since have doors need a substantial structure to support them (it is not just a couple of hinges). Unfortunately the more structure means the more reflective surfaces. 

 

Over the years, the two major players in the industry were IAC (industrial acoustics corp) and Eckel Industries. The one in the pictures above looks very much like an IAC chamber. 

 

Good luck,

-Tom

 

[Islander]

On 3/24/2020 at 2:09 PM, CECAA850 said:

I've been in it a few times.  It's pretty cool.  If you fart in there no one can hear it however it can still be detected...............

 

Q:  why do farts smell?

 

A:  for the benefit of the deaf...

[Islander]

On 3/24/2020 at 7:55 PM, Randyh said:

how does this chamber compare to others in the industry ,as we speak -- is it the only one of it's kind -

 

The National Research Council in Ottawa has its own anechoic chamber.  Paradigm uses it to help develop their speakers, which certainly must help their sound.

 

Also, why doesn’t this forum have a Wow! button?  Sometimes I’m very impressed by something, and Like is really inadequate.

[Islander]

Does anyone know what those big wedges are made of?  It looks like wood, but you’d think that would be too reflective.

 

Also, is there anyone in the room while a speaker is being tested, or is there only a calibrated microphone (or microphones) in there with the speaker during a test?

[WMcD]

Often the wedges are made of metal screening which is acoustically transparent and stuffed with fiberglass insulation which is absorptive.

 

The wedge shap prevents the creation of standing waves at any one frequency and inceases the effective surface area.

 

There is no reason for anyone to be inside during a test because a body could affect the meaurement.  The possibility of hearing damage should be a concern, always.

[CECAA850]

4 hours ago, Islander said:

Does anyone know what those big wedges are made of?

In Hope, the wedges appeared to be wire screen with a type of hard foam type material on the inside.

[PrestonTom]

1 hour ago, CECAA850 said:

In Hope, the wedges appeared to be wire screen with a type of hard foam type material on the inside.

Those look like IAC wedges, which are made of fiberglass of a specific density etc. There is usually a pole inside them to lend support and the wall-side of the pole has structure which in turn allows it to be snapped into a grid of "J -channel". This grid is attached to the concrete walls, ceiling and floor. The metal wire on the outside of each wedge is called hardware cloth and provides support so the wedges don't droop over time. The IAC chambers I have been involved with had wedges of about 30 inches in depth. This gave anechoic specs down to about 100-125 Hz. 

 

Some wedges are made out of a special foam rubber (open cell and I forget the density or porosity). These were frequently used by Eckel Industries and others. The design of these things has changed over the years. 

 

Off the top of my head, I can think of over a dozen research labs with large anechoic chambers. As a fun fact: the wedges themselves are fairly expensive (and there are hundreds of them). So when a chamber is torn down (as what happened at MIT), they actually strip out the old wedges and re-use them in another build.

[dtel]

On 3/25/2020 at 10:52 AM, babadono said:

They will not even turn out the lights when visitors are there for fear some will loose their balance, get disoriented and fall and injure themelves or others.

I asked about this and I was told something I never realized.

 

We use our eyes as much as our hearing and inner ear for balance, with the chamber removing reflected sounds we are left with the inner ear and mostly eyes for balance. So we get disoriented quicker.

It is a very cool room to go in. Once while waiting for a meeting to end I sat inside for a while, it gets odd, you get a strange feeling after a while. The door was open but no one was around, there was no noise outside or in. 

 

@JRH 

 

 

[Islander]

You weren’t tempted to do a bit of beatboxing while you had the room to yourself?